US3361979A - Apparatus for the detection of the slope of an electric signal - Google Patents

Apparatus for the detection of the slope of an electric signal Download PDF

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Publication number
US3361979A
US3361979A US352564A US35256464A US3361979A US 3361979 A US3361979 A US 3361979A US 352564 A US352564 A US 352564A US 35256464 A US35256464 A US 35256464A US 3361979 A US3361979 A US 3361979A
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United States
Prior art keywords
signal
output
slope
converter
voltage
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Expired - Lifetime
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US352564A
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English (en)
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Luttik Co
Schuringa Albertus
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Shell USA Inc
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Shell Oil Co
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J1/00—Photometry, e.g. photographic exposure meter
    • G01J1/42—Photometry, e.g. photographic exposure meter using electric radiation detectors
    • G01J1/44—Electric circuits
    • G01J1/46—Electric circuits using a capacitor
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
    • G01J3/00—Spectrometry; Spectrophotometry; Monochromators; Measuring colours
    • G01J3/28—Investigating the spectrum
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
    • G01N30/02—Column chromatography
    • G01N30/86—Signal analysis
    • G01N30/8624—Detection of slopes or peaks; baseline correction
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
    • G01R19/12—Measuring rate of change
    • G—PHYSICS
    • G06—COMPUTING OR CALCULATING; COUNTING
    • G06G—ANALOGUE COMPUTERS
    • G06G7/00—Devices in which the computing operation is performed by varying electric or magnetic quantities
    • G06G7/12—Arrangements for performing computing operations, e.g. operational amplifiers
    • G06G7/18—Arrangements for performing computing operations, e.g. operational amplifiers for integration or differentiation; for forming integrals
    • G06G7/184—Arrangements for performing computing operations, e.g. operational amplifiers for integration or differentiation; for forming integrals using capacitive elements
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03K—PULSE TECHNIQUE
    • H03K9/00—Demodulating pulses which have been modulated with a continuously-variable signal
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
    • G01N30/02—Column chromatography
    • G01N30/86—Signal analysis
    • G01N30/8603—Signal analysis with integration or differentiation
    • G01N30/8606—Integration

Definitions

  • the invention relates to a method and apparatus for the detection of the slope of an electric signal.
  • the invention has particular application where the signal concerned is one whose value as a function of another condition, for example time, is known. If the signal to be detected should not be an electric one, it can, by means well known in the art be converted into a corresponding electric signal, as a result of which it becomes accessible to the method and can be handled by the apparatus according to the invention.
  • Detection of the slope of a signal is frequently employed in the automatic processing of results of various chemical and physical analyses, for instance, spectrometric or chromatographic analyses.
  • the signal obtained in such analyses contains one or more peaks, each peak or group of peaks being characteristic of a given component or structural group present in the starting mixture.
  • the processing of the analytical results may comprise, for instance, recording, integration or control of a process condition on the basis of the analysis processed. It is not, however, always essential for all the peaks of the signal obtained to be included in the further processing. If such is the case, it then becomes necessary to switch the processing apparatus on and off each time the desired peak appears and disappears again. If the signal consists of a single peak it may also be desirable to have the processing apparatus switched on only when the peak is present.
  • a control voltage must be derived from the electric signal which is then applied to a switching device, such as, for example, a relay, a fiip -flop, or a breakdown device.
  • a known procedure for initiating the proper switching is to detect the slope of the electric information signal by passing this signal to a dilferentiating circuit, mostly including an amplifier. This produces a signal which is the the derivative of the original signal with respect to the time, which sgnal is then used to control a switching device.
  • the control signals so derived contain disturbances referred to as noise. This is true in particular for signals originating from chromatographic or spectrometric analyses, owing to the use of such detecting devices as flameionization detectors or heat-conductivity cells which generate additional noise.
  • Noise can be characterized as an alternating voltage of variable frequency and variable amplitude.
  • incidental voltage surges and more continuous alternating voltages, such as hum may also occur as disturbances in the signal. 1
  • a lower limit for the value of the signal can be determined at which the switching device can still be controlled unequivocally by a control voltage derived from the signal. This lower limit should be kept as low as possible in order to permit small signals and signals having a gentle slope to be handled. With the difierentiating circuit with amplifier mentioned hereinabove, the lower limit of the signal that can still be handled appears to lie at 20-30 ,uV. per second.
  • the invention provides a means of considerably reducing the lower limit of the signal that can still be.
  • the slope detector handled by the slope detector by insuring that only a very small proportion of the disturbances often already present in the signal can penetrate to the control voltage.
  • the electric signal is first converted into a pulsating voltage from which the control voltage is derived.
  • a pulsating voltage for the conversion of the electric signal into a pulsating voltage, use can be made of any appropriate type of converter well known in the art which converts amplitude to pulse frequency.
  • a capacitor is charged by the electric signal, either with or without use of an operational amplifier.
  • an amplifier stage can be inserted between the signal source and converter.
  • the number of pulses per unit time increases with the instantaneous value of the electric signal. In general pulses of about equal value are obtained. With the aid of filter devices the pulses can be given a desired shape.
  • a motor with an interrupter such as is also well known in the art.
  • the electric signal generally after having been amplified, is passed to a motor, the speed of which is proportional to the amplitude of the electric signal.
  • the interrupter which is coupled to the shaft of the motor, produces the pulsating voltage; a given angular displacement of the shaft being necessary for the production of the next pulse.
  • the influence of disturbances in the electric signal on the moment ,when the next pulse is produced therefore becomes smaller as the time interval between two consecutive pulses becomes larger. This is again the case at small values of the electric signal.
  • the motor with interrupter is equally effective in rendering disturbances less harmful as the converter described hereinbefore.
  • the same effect of disturbances becoming less harmful at smaller values of the signal can also be attained with a converter based on the generation of a signal by mixing the output signals of two oscillators, the frequency of at least one of these oscillators being dependent on the instantaneous value of the electric signal.
  • the generation of a pulse is governed by the attainment of, for example, the maximum value of the voltage of the differential frequency resulting from the two interferring oscillator outputs. Accordingly, as more time is required for this value to be reached, the disturbances will have a greater chance of compensation and, hence, will have less influence on the moment a pulse is generated.
  • the pulsating voltage is integrated and subsequently differentiated and the resulting signal is then used to control the switching device.
  • This enables actions to be initiated, via the switching device, at the moment when the electric signal appears, when it reaches its maximum value and when it disappears.
  • An action can also be initiated if desired when a preset maximum value of the electric signal is reached, as may occur if two peaks overlap.
  • the control signal resulting from integration and differentiation of the pulsating voltage will result in an accurate control of the switching device since at the said three particular values of the electric signal mentioned above rapid changes in the control signal are obtained.
  • a memory preferably a magnetic memory such as a magnetic tape recorder.
  • a known procedure for signal processing is to record signals in this way and then play them back later for further processing. By recording at a low tape speed and playing back at a high tape speed, signals of small values or with slowly changing values in particular .can be processed more accurately. This procedure can also be used in the detection of the slope of a signal according to the invention, which results in a further increase in accuracy.
  • the original signal can be made visible again on a recorder or an oscilloscope. In certain cases a non-linear recording may be attractive, for instance with signals that vary widely in amplitude.
  • FIGURE 1 is a schematic diagram of a signal processing system incorporating the invention
  • FIGURE 2 is a schematic diagram of a specific embodiment of a slope detector according to the invention.
  • FIGURE 3 is a diagram showing thewaveforms at various portions of the embodiment shown in FIGURE 2.
  • FIGURE 1 there is shown a system according to the invention for analyzing the signals from a chromatographic analysis of a product or mixture.
  • the mixture or product to be analyzed is passed via conduit 1' to any convenient chromatographic detector 2 which generates a pulse proportional to the quantity of the particular component being monitored which is present in the product or mixture.
  • the mixture being analyzed leaves the chromatographic detector via the conduit 3.
  • the electrical pulses generated by the chromatographic detector 2 are first amplified in an amplifier 4 and then fed to an amplitude to pulse-frequency converter 5 wherein each of the electrical peak signals is converted into, a train of pulses, the number of pulses per unit time being proportional to the instantaneous amplitude of the signal.
  • the output pulse train from the converter 5 is passed to a counter 6 which counts the pulses in the pulse train and produces an output signal proportional thereto.
  • the output signal from the counter 6 is passed via a control circuit 7, whose function will be more clearly explained below, to any desired storage device such as the printer 8.
  • the output pulse train from the converter 5 is also passed to an integrator 9 which has a long time constant relative to the duration of the individual pulses put out by the converter 5.
  • the output signal from integrator 9, after proper filtering or smoothing if necessary, is then passed via a dilferentiator 10 to a switching device '11 which is responsive to the output signal of differentiator 10 to produce an output signal corresponding to the start, maximum and end, or any other combination of these points, of the original peak signal entering the converter 5.
  • the output signal from switching device 11 is then utilized to control the control circuit 7 which in turn controls the readout and printing of the information from the counter 6.
  • FIGURES 2 and 3 there is shown a specific embodiment of the slopedetector according to the invention.
  • the specific values of the components shown in the figure being as follows:
  • FIGURE 3b The output of converter 5, after proper shaping in the pulse shaper 13 to insure uniformly shaped pulses, appears as shown in FIGURE 3b. It should be understood that the output pulses from the converter are shown as negative pulses due to the particular configuration of the remaining circuitry but that systems according to the invention utilizing positive pulses and consequently generating signals opposite in polarity from those shown in the remaining portions of FIGURE 3 may be utilized.
  • the shaped train of pulses is then connected via an emitter-follower stage 14, which is used for impedance matching, to an integrating circuit 15 having, as mentioned above, a relatively long time constant relative to the duration of the individual pulses from the converter 5, and consisting of diode D a capacitor C and a resistance R
  • the negative pulse train appearing at the output of the emitter-follower stage 14 is passed via the diode D to charge up the capacitor C ;the diode D preventing the charge on the capacitor C from discharging through the Resistor R
  • the signal across the capacitor C would normally result in an everincreasing staircase type wave due to the relatively long time constant of the integrating circuit, in the instant example about 0.4 second, the output signal across the capacitor C resulting from the pulsetrain will, instead of an everincreasing staircase wave, result in a peak type wave having a staircase shaped envelope.
  • data processing equipment i.e. printer 8 may be connected to the terminals A and B which are connected across capacitor C
  • the voltage signal across the capacitor C is fed via another emitter-follower stage 16 for impedance matching to a filter 17 where the staircased envelope peak is smoothed resulting in the Waveform shown in FIGURE 3c.
  • the output of the filter 17 is a wave having a shape similar to that of the original peak but having steeper slopes at its start and end. This is caused by the relatively long time between pulses applied to the capacitor which correspond to low amplitudes of the original signal peak.
  • the output signal from the filter 17 is applied via another emitter-follower stage 18, again for impedance matching, to a differentiating circuit 19 consisting essentially of a capacitor C and the coil 22 of a polarized relay 23 which forms the output switching device of the slope detector.
  • the resistors R and R condensers C and C and diodes D are provided to reduce any noise in the current applied to the difierentiator due to frequency jitter occurring in the voltage to frequency converter and to protect the relay 23 against overloading.
  • Polarized relay 23 which is actuated by the current through the condenser C and hence the time dilferential of the voltage output signal from emitter-follower stage 18, consists of a relay having a center stable contact 24 and two make contacts 25 and 26. Closure of the contact 24 with the contact 25 or 26 is affected when a small positive or a small negative current is passed through the coil 22. These levels of current are indicated as dotted lines 29 and 30 in FIGURE 30'. Because of the relatively steep slope of the curve shown in 3d, closure of the contacts 24 and 25 at a level corresponding to dotted line 29 indicates the start of the original peak (FIGURE 3a). As shown in FIGURE 36, contacts 24 and 25 remain closed as long as the current is above the level indicated by line 29.
  • Example 2 In order to illustrate the improved results obtained with a slope detector according to the invention over the prior art type of slope detector, comparison tests were made using a slope detector as shown in FIGURE 2 and a differentiating type of slope detector as known in the prior art and utilizing electrical signals produced by a peak voltage generator.
  • the peaks produced had dilferent maximum values but a constant width of 100 seconds, with each peak having approximately the shape of a Gaussian curve.
  • the results of these comparison tests indicating the maximum value of the peak signals at which the respective slope detectors respond or do not respond are shown below.
  • the slope detector according to the invention still responds to a signal of a value about 10 times smaller than a detector according to the prior art.
  • Apparatus for the detection of a slope of an electrical peak signal comprising:
  • integrator means connected to the output of said amplitude to pulse-frequency converter for integrating the train of output pulses from said converter, said integrator means having a relatively long time constant with respect to the duration of the individual pulses at the output of said converter;
  • switch means connected to the output of said differentiating circuit and responsive to the output signal therefrom for producing an indication corresponding to the start, maximum and end of said electrical peak type signal.
  • said integrating 7 means comprises: a diode having one electrode connected to the output of said amplitude to pulse-frequency converter and having the second electrode thereof connected to a capacitor and a resistance connected in parallel.
  • said integrating 5 means comprises a diode having one electrode connected to theoutput of said converter and the other electrode connected to a capacitor and resistance connected in parallel.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Mathematical Physics (AREA)
  • Theoretical Computer Science (AREA)
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US352564A 1963-03-21 1964-03-17 Apparatus for the detection of the slope of an electric signal Expired - Lifetime US3361979A (en)

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NL290465 1963-03-21

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US (1) US3361979A (enrdf_load_stackoverflow)
DE (1) DE1283382B (enrdf_load_stackoverflow)
GB (1) GB1030808A (enrdf_load_stackoverflow)
NL (1) NL290465A (enrdf_load_stackoverflow)

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3531633A (en) * 1965-06-29 1970-09-29 Marathon Oil Co Integrating apparatus using voltage to frequency converter
US3594726A (en) * 1968-09-30 1971-07-20 Nester & Faust Mfg Corp Programmed slope and amplitude responsive system
JPS4910645A (enrdf_load_stackoverflow) * 1972-05-24 1974-01-30
US3872728A (en) * 1972-10-10 1975-03-25 Michael F Joyce Electronic temperature measuring instrument
WO2003065058A1 (de) * 2002-02-01 2003-08-07 Infineon Technologies Ag Schaltkreis-anordnung, redox-recycling-sensor, sensor-anordnung und verfahren zum verarbeiten eines über eine sensor-elektrode bereitgestellten stromsignals
EP1315964A4 (en) * 2000-09-08 2008-09-24 Waters Investments Ltd METHOD AND DEVICE FOR DETERMINING THE LIMITS OF A DETECTION PROFILE AND FOR CONTROL PROCESSES (20.03.02)
EP2073384A3 (en) * 2007-12-21 2013-12-18 Power Integrations, Inc. Method and apparatus for time-differential comparison of an analog signal
US20150185343A1 (en) * 2012-07-06 2015-07-02 Cgg Services Sa Seismic source array calibration and synchronization method, apparatus and system

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2547978A (en) * 1945-05-16 1951-04-10 Clifford M Ryerson Transient peak voltmeter
US3068418A (en) * 1958-12-30 1962-12-11 Textron Electronics Inc Amplitude limiter employing integrating, clipping and differentiating circuits in series
US3251053A (en) * 1962-11-02 1966-05-10 Doong Henry Analog to digital converter

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2431915A (en) * 1946-09-20 1947-12-02 Robert D Burchfield Bridge unbalance indicating means
FR1231829A (fr) * 1959-04-16 1960-10-03 Compteurs Comp D Dispositif électrique de mesure des variations lentes de tensions continues faibles

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2547978A (en) * 1945-05-16 1951-04-10 Clifford M Ryerson Transient peak voltmeter
US3068418A (en) * 1958-12-30 1962-12-11 Textron Electronics Inc Amplitude limiter employing integrating, clipping and differentiating circuits in series
US3251053A (en) * 1962-11-02 1966-05-10 Doong Henry Analog to digital converter

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3531633A (en) * 1965-06-29 1970-09-29 Marathon Oil Co Integrating apparatus using voltage to frequency converter
US3594726A (en) * 1968-09-30 1971-07-20 Nester & Faust Mfg Corp Programmed slope and amplitude responsive system
JPS4910645A (enrdf_load_stackoverflow) * 1972-05-24 1974-01-30
US3872728A (en) * 1972-10-10 1975-03-25 Michael F Joyce Electronic temperature measuring instrument
EP1315964A4 (en) * 2000-09-08 2008-09-24 Waters Investments Ltd METHOD AND DEVICE FOR DETERMINING THE LIMITS OF A DETECTION PROFILE AND FOR CONTROL PROCESSES (20.03.02)
WO2003065058A1 (de) * 2002-02-01 2003-08-07 Infineon Technologies Ag Schaltkreis-anordnung, redox-recycling-sensor, sensor-anordnung und verfahren zum verarbeiten eines über eine sensor-elektrode bereitgestellten stromsignals
US20060292708A1 (en) * 2002-02-01 2006-12-28 Alexander Frey Circuit arrangement, redox recycling sensor, sensor assembly and a method for processing a current signal provided by a sensor electrode
EP2073384A3 (en) * 2007-12-21 2013-12-18 Power Integrations, Inc. Method and apparatus for time-differential comparison of an analog signal
US20150185343A1 (en) * 2012-07-06 2015-07-02 Cgg Services Sa Seismic source array calibration and synchronization method, apparatus and system
US9606253B2 (en) * 2012-07-06 2017-03-28 Cgg Services Sas Seismic source array calibration and synchronization method, apparatus and system

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DE1283382B (de) 1968-11-21
NL290465A (enrdf_load_stackoverflow)
GB1030808A (en) 1966-05-25

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